System and method for shimming a bevel gear in an IGB on a gas turbine without removal of the bevel gear

ABSTRACT

A method for shimming a thrust bearing for an accessory power take off shaft to obtain optimal meshing of bevel gears within the internal gearbox (IGB) without disassembly of the IGB is enabled by relocating the thrust bearing from the engine sump. The accessory gearbox (AGB) is driven from a power off-take from the turbine spool via the IGB. The radial position of the power take-off bevel gear is established by a radial position of the thrust bearing attached to the exterior of the casing via a housing. Candidate shims are selected from a set each having different thicknesses, the shims are formed of two halves and placed between the housing and the engine casing to adjust the radial position of the thrust bearing and consequently the power take-off bevel gear, without requiring the disassembly of the IGB.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a divisional application of, and claims priorityunder 35 USC § 120 to U.S. nonprovisional application Ser. No.16/557,048, filed Aug. 30, 2019, the entire contents of which areincorporated by reference.

BACKGROUND

In gas turbine engine applications, torque is transmitted from theturbine spool, typically the high pressure spool, to drive engineaccessories, such as generators, hydraulic and oil pumps, etc. Thetorque is typically transferred to a shaft perpendicular to the mainaxis of the turbine spool. This orthogonal diversion of torque isachieved via a set of bevel gears in the Internal Gear Box (IGB). TheIGB includes a main axis bevel gear interacting with the accessory bevelgear, the accessory bevel gear connected to the accessory shaft which inturn transfers the torque from the IGB to an Accessory Gear Box (AGB).

FIG. 1 illustrates a conventional arrangement within the IGB. The mainaxis bevel gear 103 rotates about the main axis 101 of the turbinespool, in this case a high pressure spool (not shown), alternatively thelow pressure spool (also not shown) may be used. The accessory bevelgear 105 meshes (cooperates) with the main axis bevel gear 103 totransfer torque through the accessory torque transfer shaft 111. Thetransfer shaft 111 typically engages a spline within the AGB (notshown). The transfer shaft 111 is typically orthogonal to the main axis.

In order to achieve the optimal mesh between the teeth of the main axisbevel gear 103 and the accessory bevel gear 105, the radial position ofthe accessory bevel gear 105 is adjusted with the use of shims. As shownin FIG. 1 , the shims 109 are assembled adjacent and below to the gear'sthrust bearing 107 as it is the thrust bearing 107 that dictates radialposition. The shims 109 change the radial position of the thrust bearing107 and thus the accessory bevel gear 105 with respect to the main axisbevel gear 103 by defining the radial distance between an inter surfaceof the casing 113 and the radially outer seat of the thrust bearing 107.The use of axial and radial within the context of this disclosure iswith reference to the turbine spool, axially being parallel to the mainaxis and radially being orthogonal thereto.

Conventionally, the thrust bearing 107 is placed in the sump area closeto the accessory bevel gear 105 within the IGB. This favorable positionalso unloads the torque transfer shaft 111 via the thrust bearing 107 ofcompressive and lateral forces and thus facilitates the use of a smallerand/or lighter shaft, as the sizing of the shaft 111 becomespredominately a function of torque. Consequently, because of thislocation within the engine sump, assemblers must repeatedly insert andremove the bevel gears 103, 105, transfer shaft 111 and the thrustbearing 107 from the forward casing 113 during the shimming processuntil the desired bevel gear mesh tooth patterns and optimum backlash isachieved. This assembly and disassembly may add a half a day to a day tothe engine assembly process, which is also attendant with an increase incosts and heightened risk of collateral damage to the engine parts.

Thus there is a need in the art for a system and method in which therepeated assembly and disassembly is reduced or eliminated in thepositioning of the accessory bevel gear. The disclosed subject matterintroduces a system and method in which the shimming process may beaccomplished from the exterior of the casing, thus eliminating therepeated assembly and disassembly of the bevel gears. The disclosedsubject matter also introduces the use of a split shim, such that theshims may be installed with only minor disassembly of casing externalcomponents.

SUMMARY

According to some aspects of the present disclosure, a system fordriving an accessory gearbox associated with a gas turbine engine, mayinclude a turbine spool defining a main axis; an engine casing definingan interior volume. The accessory gearbox may be external to the enginecasing. Embodiments include an accessory torque transfer shaft, whichmay define a shaft axis anti-parallel to the main axis and an internalgearbox within the casing. The internal gearbox may contain a bevel gearconnected to the turbine spool and a cooperating bevel gear connected tothe accessory torque transfer shaft. Embodiments may include a thrustbearing connected to the accessory shaft at a predetermined positionalong the shaft axis; a flange assembly connected to the thrust bearing.Thrust may be transferred from the torque transfer shaft to the thrustbearing and to the flange assembly. Embodiments include a shimpositioned between an exterior surface of the engine casing and theflange assembly (or housing). The thickness of the shim may establishthe radial positioning of the thrust bearing with respect to the casing.

In some embodiments, the shaft axis is perpendicular to the main axisand the flange assembly connects the accessory gearbox to the enginecasing. The system may further include a second bearing located on thetorque transfer shaft between the corresponding bevel gear and thethrust bearing, the second bearing transferring axial force from thetorque transfer shaft to the casing. The casing further defines a radialpassage between the interior volume and the exterior of the enginecasing, the radial passage having an internal diameter greater than adiameter of the accessory torque transfer shaft and less than thelargest diameter of the flange assembly. Shims may be formed of twohalves. In some embodiments, the two halves are asymmetric with respectto each other. In some embodiments, each of the halves have a pluralityof holes, the plurality of holes forming a pattern unique to eachrespective half. The system may further include a plurality of shims,each of the plurality of shims having a thickness at least differentfrom another of the plurality of shims.

Other aspects of the present disclosure include a method for the radialpositioning of a power take-off bevel gear with respect to a bevel gearassociated with a turbine. The method may include positioning the powertake-off bevel gear within an interior of an engine casing, extendingthe transfer shaft associated with the power take-off bevel gear betweenthe bevel gear and the exterior of the casing; attaching a thrustbearing to a flange assembly and from the exterior of the casing slidingthe thrust bearing and flange assembly over the transfer shaft in theradially inward direction. The method further includes placing twohalves of a shim plate around the flange assembly between a radiallyinward facing surface of the flange assembly and a radially outwardfacing exterior surface of the casing; applying a radial force to theflange assembly to thereby engage the flange with the shim plate and theshim plate with the exterior surface to the casing. The method alsoincludes determining a radial position of the take-off bevel withrespect to the turbine bevel; placing two halves of another shim aroundthe flange assembly and between the radially inward facing surface ofthe flange assembly and the radially outward facing exterior surface ofthe casing to change the radial position of the take-off bevel. Thethrust bearing may engage the transfer shaft at a predetermined locationalong the transfer shaft.

In some embodiments, the step of extending the transfer shaft includesextending the transfer shaft through a second bearing located in theinterior of the casing. The second bearing transfers axial loads fromthe transfer shaft to the casing. In some embodiments, the step ofplacing two halves of another shim may further include selecting a shimplate from a plurality of shim plates, the selection being a function ofat least the determined position of the power take-off bevel gear. Thestep of placing two halves of another shim may further comprise removingthe two halves of the shim plate or may include placing the two halvesof the another shim on top of the two halves of the shim already inplace.

Some aspects of the present disclosure include a method of adjusting theradial position of the take-off bevel gear with respect to the drivingbevel gear from a first position to a second position without outremoving the take-off bevel gear or the transfer shaft from theirengaged position. The method may include selecting a candidate shim froma plurality of shims having different thicknesses; placing the candidateshim radially between a portion of the housing and the casing; advancingthe thrust bearing and housing over the transfer shaft; wherein theadjustment of the radial position is a function of the candidate shimthickness.

In some embodiments, the housing is a portion of the accessory gearbox.In some embodiments, the step of placing the candidate shim radiallybetween a portion of the housing and the casing, further comprisesplacing two halves of the candidate shim between the portion of thehousing and the casing, and wherein the housing is not removed from thetransfer shaft during the placement of the two halves. The radialposition of the take-off bevel gear may be further adjusted by selectinga second candidate shim from the plurality of shims and placing thesecond candidate shim between the housing and the casing.

BRIEF DESCRIPTION OF THE DRAWINGS

The following will be apparent from elements of the figures, which areprovided for illustrative purposes.

FIG. 1 is an illustration of a prior art system for positioning theaccessory bevel gear.

FIG. 2 is an illustration of a bevel gear system according toembodiments of the disclosed subject matter.

FIG. 3 is a partial exploded view of the bevel gear assembly and shimsaccording to embodiments of the disclosed subject matter.

FIGS. 4A and 4B are isolated illustrations of the shims according toembodiments of the disclosed subject matter.

FIG. 5 is a flow chart of the shimming process according to embodimentsof the disclosed subject matter.

The present application discloses illustrative (i.e., example)embodiments. The claimed inventions are not limited to the illustrativeembodiments. Therefore, many implementations of the claims will bedifferent from the illustrative embodiments. Various modifications maybe made to the claimed inventions without departing from the spirit andscope of the disclosure. The claims are intended to coverimplementations with such modifications.

DETAILED DESCRIPTION

For the purposes of promoting an understanding of the principles of thedisclosure, reference will now be made to a number of illustrativeembodiments in the drawings and specific language will be used todescribe the same.

FIG. 2 discloses an arrangement of the bevel gears and thrust bearing207 which eliminates the requirement to disassemble the gears in theshimming process according to an embodiment of the disclosed subjectmatter.

In the embodiment shown in FIG. 2 , the radial position of the accessorybevel gear 205 is adjusted with the use of shims 209. As shown in FIG. 2, the shims 209 are assembled adjacent and below to the gear's thrustbearing 207. The thrust bearing 207 dictates radial position of theaccessory bevel gear 205 as noted previously. Unlike the conventionalarrangements, the shims 209 change the radial position of the thrustbearing 207 and thus the accessory bevel gear 205 with respect to themain axis bevel gear 203 by defining the radial distance between anouter surface 231 of the casing 213 and a radially inward facing surface243 of housing 241. The housing 241 seats the thrust bearing 207. TheAGB 221 is attached to the casing 213 by or via housing 241.

In FIG. 2 , the thrust bearing 207 is not located in the sump area withthe accessory bevel 205 but rather at the opposite end proximate to theexterior of the casing 213. This relocation to the bottom or radiallyoffset position with respect to the accessory bevel gear 205 andtransfer shaft 211, places the thrust bearing 207 near theengine-accessory gearbox (AGB) split-line. This location requiresaddressing the additional load carried by the accessory transfer shaft211, specifically with respect to axial loading along the shaft axis 215due to the thrust loading. Although moving the location of the thrustbearing away from the mesh, gives less control of the gear patterns.Design mitigations such as material selection, shaft length, powertake-off load can be made to minimize such concern. A bearing 217 isalso shown in FIG. 2 , similarly situated as in the prior art, howeverbearing 217 is not a thrust bearing and only transfers axial forcestransverse to the transfer shaft from the shaft 211 to the casing 213.Additional non-thrust bearings may also be incorporated elsewhere on thetransfer shaft 211 as needed, for example to mitigate overload of thetransfer shaft 211.

Advantageously, because of the location outside of the sump, assemblersneed not remove the accessory bevel gear 205 in order to adjust theradial position by adding or changing shims 209. Instead, while leavingthe elements of the IGB in place (i.e. main axis bevel gear 203 andaccessory bevel gear 205) the shims 209 may be placed between the casing213 and the housing 241 (flange assembly) with access being external tothe casing. Furthermore, with the split configuration of the shims 209(described in more detail in FIG. 4 below), the housing 241 need not beentirely removed from the casing 213, but only slid radially outward tocreate a separation between the casing the inner face surface 243 enoughto remove a shim or insert a different shim. FIG. 3 discussed belowfurther illustrates this embodiment.

The thrust bearing 207 attaches to the transfer shaft 211 at apredetermined location along the axis 215, as shown in FIG. 2 a ridge orflare 219 is provided on the transfer shaft to seat the top of thethrust bearing 207 to the transfer shaft 211. The casing 213 defines aradial passage 218 between the interior in which the sump and IGB arelocated and the exterior of the casing 213, the radial passage 218 hasan internal diameter of sufficient size to accommodate the transfershaft 211, with the internal diameter be constricted to allow thepositioning of the shims 209 between the casing 213 (i.e. less than thediameter of the housing 241 which remains external to the casing 213.

With the thrust bearing 207 relocated to the bottom of the transfershaft 211, the shim 209 location is no longer buried within the sump andis readily accessible reducing the time and expense of disassembly andassembly of the conventional method.

In FIG. 2 , the transfer shaft axis 215 is shown perpendicular to themain axis 201; however, other orientations (i.e. oblique angles) arealso envisioned.

FIG. 3 illustrates an embodiment in which the shim 309 is formed inhalves 309 a and 309 b, and thus allows the insertion and/or removalwithout disassembling the bevel gears or entirely removing the housing341. By slightly siding the housing 341 radially outward (downward) overthe transfer shaft 311, the halves of the shim 309 may be insertedbetween the flange of the housing 341 and the exterior surface of thecasing 313. The housing 341 may then be slid radially inward (upward)and secured to the casing 313.

This arrangement along with the two-piece shim 309 eliminates the needto repeatedly remove and replace the bevel gear 305 during engineassembly.

FIG. 4 is an illustration of the split shims according to an embodimentof the disclosed subject matter. The shims 409 each have a plurality ofholes 451 and grooves 453, which correspond the bolts used to attach thehousing 341 and/or the AGB to the casing 313. The layout of the holes451 and grooves 453, as well as the perimeter of the shim 409 ispreferable asymmetric and/or irregular (i.e. each of the halves haveholes and groove that form a unique pattern) such that the each of theshim halves 409 a and 409 b will only fit in one position (i.e. 409 awill not fit on the side designated for shim half 409 b, nor will eitherfit if inserted upside down.) Each of the halves 409 a and 409 b havethe same predetermined thickness, which may be stamped or otherwiseindicated on the shim 409. Additionally, each turbine engine duringassembly may be provided with a set having a plurality of shims ofdifferent thicknesses. The assembler may run through several candidateshims until the proper radial positioning of the accessory bevel gear305 is met. Multiple shims may be stacked to obtain the desiredpositioning or the selection of a single shim of proper thickness may berequired. While FIGS. 4A and 4B illustrate the shim 409 divided into twohalves 409 a and 409 b, additional divisions are equally envisioned, forexample where access to the housing 341 is limited to a width less thanthe width of the shim 409, in which case the shim 409 may be made ofthirds, each having a width that allows access to the housing 341.

FIG. 5 is an illustrative flow chart 500 of the shimming processaccording to embodiments of the disclosed subject matter. Reference ofthe components are with respect to FIG. 2 . The power take-off bevelgear 205 is positioned and meshed with the main axis bevel gear 203within the interior of an engine casing 213 as shown in Block 501. Withthe power take-off bevel gear 205 in position, the transfer shaft 211associated with the power take-off bevel extends between the bevel gear205 and the exterior of the casing 213. The transfer shaft 211 may alsoextend through a second bearing (non-thrust bearing) 217 located in theinterior of the casing 213. This second bearing 217 allows relativeaxial movement along the shaft axis 215 between the bearing 217 and thetransfer shaft 211 and only reacts lateral forces (i.e. forcesperpendicular to the shaft axis 215).

The thrust bearing 207 is attached to a housing 241 (flange assembly)and from the exterior of the casing 213, the housing 241 and attachedthrust bearing 207 are slid over the transfer shaft 211 in the radiallyinward direction as shown in Block 503.

The two halves of a shim 209 are placed around the housing 241 between aradially inward facing surface 243 of the housing 241 and a radiallyoutward facing exterior surface of the casing 213 as shown in Block 505.Alternatively, if a split shim is not used, the shim 209 may be placedover the housing 241 prior to placing the housing 241 over the transfershaft 211, in which case any subsequent change of shims would likewiserequire the housing 241 to be removed. In either alternative, thehousing 241 is forced into place engaging the housing 241 with the shim209 and the shim 209 with the exterior surface to the casing 213 asshown in Block 507.

The radial position of the power take-off bevel 205 with respect to theturbine spool bevel 203 is evaluated to ensure the proper operation ofthe IGB as shown in Block 509. If the position is required to bechanged, the housing is slid radially outward from the casing to allowthe placement of two halves of a new shim around the housing 241 betweenthe radially inward facing surface 243 of the housing 241 and theradially outward facing exterior surface of the casing, as shown inBlock 511. The old shim may be removed prior to placing the new shim, orthe new shim may be stacked upon the old shim. Typically, depending onthe amount of change required from the old position, an assembler willselect a candidate shim from a set provided with the turbine, which willresult in the proper positioning, rather than stacking shims. Thehousing again is forced into place engaging the housing 241 with theshim 209 and the shim 209 with the exterior surface to the casing 213and resulting in the proper radial positioning of the power take-offbevel 203. The thrust bearing engages the transfer shaft at thepredetermined location 219 along the transfer shaft 211 to transfer thethrust load to the casing 213. The process may be repeated as needed toachieve optimal mesh.

Although examples are illustrated and described herein, embodiments arenevertheless not limited to the details shown, since variousmodifications and structural changes may be made therein by those ofordinary skill within the scope and range of equivalents of the claims.

What is claimed is:
 1. A method for a radial positioning of a powertake-off bevel gear with respect to a turbine spool bevel gearassociated with a turbine spool, the method comprising: positioning thepower take-off bevel gear within an interior of a casing, extending atransfer shaft associated with the power take-off bevel gear between theturbine spool bevel gear and an exterior of the casing; attaching athrust bearing to a flange assembly, sliding the thrust bearing and theflange assembly from the exterior of the casing over the transfer shaftin a radially inward direction; placing a shim plate between a radiallyinward facing surface of the flange assembly and a radially outwardfacing exterior surface of the casing to change a radial position of thepower take-off bevel gear; applying a radial force to the flangeassembly to thereby engage the flange assembly with the shim plate andthe shim plate with the exterior surface of the casing to change theradial position of the power take-off bevel gear; and determining theradial position of the power take-off bevel gear with respect to theturbine spool bevel gear; wherein the thrust bearing engages thetransfer shaft at a predetermined location along the transfer shaft,wherein the flange assembly is disposed between and directly contacts aradially outer wall of the thrust bearing and the casing.
 2. The methodof claim 1, wherein the step of extending the transfer shaft furthercomprises extending the transfer shaft through a second bearing locatedin the interior of the casing.
 3. The method of claim 2, wherein thesecond bearing transfers lateral loads from the transfer shaft to thecasing.
 4. The method of claim 1 wherein the shim plate is a first shimplate, the method further comprises placing a second shim plate betweenthe radially inward facing surface of the flange assembly and theradially outward racing exterior surface of the casing.
 5. The method ofclaim 4, wherein the placing the second shim plate further comprises:selecting a candidate shim plate from a plurality of shim plates, theselection being a function of at least the determined radial position ofthe power take-off bevel gear.
 6. The method of claim 4, wherein thestep of placing the second shim plate further comprises removing thefirst shim plate.
 7. The method of claim 4, wherein the placing thesecond shim plate comprises placing the second shim plate on top of thefirst shim plate.
 8. The method of claim 4 wherein the first shim plateand the second shim plate each comprise two halves.
 9. A method ofadjusting a radial position of a power take-off bevel gear in a gasturbine engine, the power take-off bevel gear coupled to an accessorygearbox, the radial position adjusted with respect to a driving bevelgear coupled to a turbine spool in the gas turbine engine from a firstposition to a second position without removing the power take-off bevelgear or a transfer shaft from their respective engaged positions,wherein the accessory gear box is driven from a power off-take from theturbine spool via an internal gear box, the internal gear box engagingthe driving bevel gear coupled to the turbine spool with the powertake-off bevel gear coupled to the accessory gear box via the transfershaft, wherein the radial position of the power take-off bevel gear isestablished by a radial position of a thrust bearing attached to anexterior of a casing of the gas turbine engine via a housing, the methodcomprising: selecting a candidate shim from a plurality of shims havingdifferent thicknesses; placing the candidate shim radially between aportion of the housing and the casing; advancing the thrust bearing andthe housing over the transfer shaft and securing the housing to thecasing, wherein the adjustment of the radial position of the powertake-off bevel gear is a function of a thickness of the candidate shim,wherein the housing is disposed between and directly contacts a radiallyouter wall of the thrust bearing and the casing.
 10. The method of claim9, wherein the housing is a portion of the accessory gear box.
 11. Themethod of claim 9, wherein the placing the candidate shim radiallybetween the portion of the housing and the casing further comprisesplacing two halves of the candidate shim between the portion of thehousing and the casing, and wherein the housing is not removed from thetransfer shaft during placement of the two halves.
 12. The method ofclaim 9, wherein the radial position of the power take-off bevel gear isfurther adjusted by selecting a second candidate shim from the pluralityof shims having different thicknesses and placing the second candidateshim between the housing and the casing.
 13. A method for a radialpositioning of a power take-off bevel gear within an internal gear boxwith respect to a turbine spool bevel gear associated with a turbinespool, the method comprising: positioning the power take-off bevel gearwithin an interior of a casing, the casing defining an engine sump andthe internal gear box disposed within the casing; extending a transfershaft associated with the power take-off bevel gear between the turbinespool bevel gear and an exterior of the casing; attaching a thrustbearing to a flange assembly, from the exterior of the casing by slidingthe thrust bearing and the flange assembly over the transfer shaft in aradially inward direction; placing two halves of a shim plate around theflange assembly between a radially inward facing surface of the flangeassembly and a radially outward facing exterior surface of the casing tochange a radial position of the thrust bearing with respect to thecasing; applying a radial force to the flange assembly to thereby engagethe flange assembly with the shim plate and the shim plate with theexterior surface of the casing; and determining a radial position of thepower take-off bevel gear with respect to the turbine spool bevel gear;wherein the thrust bearing engages the transfer shaft at a predeterminedlocation along the transfer shaft, wherein the two halves are asymmetricwith respect to each other.
 14. The method of claim 13, wherein theturbine spool defines a main axis and the transfer shaft defines a shaftaxis, wherein the shaft axis is perpendicular to the main axis.
 15. Themethod of claim 13, further comprising connecting the casing to anaccessory gear box via the flange assembly.
 16. The method of claim 13,further comprising locating a second bearing on the transfer shaftbetween the power take-off bevel gear and the thrust bearing, the secondbearing configured to transfer lateral forces from the transfer shaft tothe casing.
 17. The method of claim 13, wherein the casing defines aradial passage between the engine sump and the exterior of the casing,the radial passage having an internal diameter greater than a diameterof the transfer shaft and less than a largest diameter of the flangeassembly.
 18. The method of claim 13, wherein the shim plate is a firstshim plate, the method further comprising placing a second shim platearound the flange assembly and between the radially inward facingsurface of the flange assembly and the radially outward facing exteriorsurface of the casing.
 19. The method of claim 18, wherein the firstshim plate and the second shim plate have different thicknesses.
 20. Themethod of claim 13, wherein the each of the two halves have a pluralityof holes forming a pattern unique to each respective half.